Precise solder application onto microminiature circuit sites is considered extremely important in the manufacture of various microelectronic devices such as those used in the information handling (computer) field. Miniaturization of circuitry is, understandably, highly desired in the computer industry. Devices using such circuitry include flexible circuit members (e.g., tape automated bonded (TAB) packages), circuitized ceramic substrates, printed circuit boards, etc. Interconnection between these devices (e.g., flexible circuits and printed circuit boards) is preferably accomplished using solder material as the coupling medium. Heretofore, one known technique for applying solder onto such devices has been to use a screening process. Such a process may, however, present various problems, such as non-uniformity of solder amount application per site (e.g., lands), "solder bridges" occurring between adjacent lands causing electrical shorting therebetween in final operation, etc. Various examples of solder application procedures are described in U.S. Pat. Nos. 4,872,261 (Sanyal et al), 4,832,255 (Bickford et al), 4,684,055 (Baer et al) and 4,311,267 (Lim). In another patent, 5,048,747 (Clark et al), solder transfer is accomplished using a "shuttle" having solder therein in combination with a solder mask, the latter deemed necessary to retain the solder during deposition (to prevent undesirable bridging).
The present invention represents an improvement over known solder application processes, including those described in the above patents, by providing a heatable transfer member with precisely defined (e.g., drilled) holes therein into which solder paste is deposited. The transfer member, with solder, is precisely aligned relative to respective circuitry on a substrate (e.g., ceramic) and heated to a predetermined temperature sufficient to effect solder reflow onto the substrate's metallic sites (circuitry). Precise solder amount per site application is assured due to the initial accurate volume determination of the transfer member's holes. Ease of paste filling (into the transfer member) is also assured. Significantly, such precise solder deposition is attained without use of a solder mask or the like.
It is believed that such an improved method would constitute a significant advancement in the art.